The present invention relates to a process and device for piecing to an open-end friction spinning device having two friction spinning elements which are driven in the same direction and form a nip that is subjected to suction, in which fibers are fed into the nip, into a thread forming zone, from which they are drawn off again in the form of a continuous thread.
According to a process which is known in rotor spinning, the spinning station is supplied with a tube equipped with a winding for piecing, or lead winding when the bobbin is to be replaced (CH-PS No. 618.741), which corresponds with U.S. Pat. No. 4,125,990. To piece thread to the spinning aggregate, the thread of this piecing or lead winding is fed to the spinning aggregate and is then drawn off, whereby the piecing joint reaches the tube.
DE-OS No. 2.501.735 also teaches to separate the thread segment containing the piecing joint from the thread and to aspire it into the opening of a thread draw-off pipe. To achieve this, piecing is effected in this known art with the help of an auxiliary thread supplied from a piecing bobbin which is carried along by a travelling bobbin replacement device. Also, according to this art, the thread is first transferred to the empty bobbin and the thread segment containing the piecing joint is then separated and taken away. This means that in this state of the art a special piecing device is required for bobbin replacement, in addition to the normal piecing device.
It is therefore the task of the present invention to create a device making it possible to effect piecing by a simple method and without requiring a piecing thread. This goal is achieved with practice of this invention in that the fibers fed into the nip are twisted into a fiber bundle and in that said fiber bundle is partially conveyed out of the nip in its longitudinal direction, to be siezed at that point and to be transferred to a winding device. A piecing thread is thus not required, since the fiber bundle produced in the open-end friction spinning device is itself seized and drawn off. Thus a bobbin can be newly started without auxiliary thread which must otherwise be held in readiness on an auxiliary bobbin or on the empty tube, and the device for storing such auxiliary bobbins or devices to supply the piecing winding are not needed. The piecing process, when a bobbin is started, can be thus carried out in the simplest way possible and with little mechanical or time expenditure.
Preferably, the fiber bundle is separated from the remaining thread before the transfer of the thread to the winding device takes place. The piecing joint, constituting a defect, is thus eliminated. The thread which is now transferred to the empty spool thus does not contain any piecing joint. To achieve this goal, no flying bobbin replacement is required, so that maintenance of the spinning device can be combined with bobbin replacement without adverse effect upon the new bobbin.
In a practical version of the process according to invention, fiber feeding is switched off after the formation of the fiber bundle, the fiber bundle is then partially taken out of the nip of the friction spinning elements by pneumatic means, is seized at that point and is secured against twisting at its leading end, whereupon fiber feeding is resumed and the newly produced thread is drawn off from the nip. Through the temporary interruption of fiber feeding, individual fibers are prevented from entering the nip during pneumatic conveying of the fiber bundle, as they would otherwise leave the nip immediately. This interruption of fiber feeding does not effect secure piecing; besides, a possible shortage in fibers can be compensated for by appropriately timing the fiber bundle's staying time in the nip once its leading end has been secured against twisting by controlling the rotational speed of the friction spinning elements, etc.
Pneumatic conveying of the fiber bundle can be carried out in various manners. In a preferred version of the process according to this invention, the fiber bundle is partially pulled out of the nip by a suction air stream acting upon the draw-off side of the nip, whereupon the leading end of the fiber bundle is temporarily applied against a twist brake after it has left the nip, and is again released from the twist brake with the newly produced thread being drawn off from the nip. Alternately, it is also possible to produce a compressed air stream and to blow the fiber bundle partially out of the nip so that it can be seized.
To carry out this process, an auxiliary conveying installation to convey the fiber bundle from the thread forming zone up to the draw-off end of the friction elements is provided, as is a grabber to seize the fiber bundle leaving the nip of the friction spinning elements and to transfer the thread being formed to a draw-off device. The auxiliary conveyor ensures that the fiber bundle is presented to the grabber and is taken up while the grabber, by seizing the leading end of the fiber bundles, prevents it from rotating in the seizing zone, so that true twisting is produced in the remaining length of the fiber bundle as required in order to twist and incorporate the newly fed fibers into the thread. The newly formed thread is then transferred to a draw-off device to be drawn off continuously from the thread forming zone.
To prevent the piecing joint formed by the fiber bundle from reaching the newly inserted empty tube, the grabber can be equipped with a thread cutting device in a further embodiment of the object of the invention, by means of which this joint can be cut from the remainder of the thread.
The grabber can be designed in different ways. It is conceivable, for instance, to install a stationary grabber at the draw-off side of the open-end friction spinning elements. A transfer device can serve as the draw-off device to which the thread is fed by means of a hoop or similar device or which fetches the thread from the grabber, draws it off and presents it to the bobbin station by means of an appropriate movement. Preferably however, the grabber itself is designed to move, whereby the draw-off device rwhich receives the newly formed thread is constituted by the winding device. A simple embodiment fulfilling objects of this invention is thus achieved.
In an advantageous embodiment of the device according to this invention the grabber is fashioned as the mouth of a suction pipe in front of which a twist brake is installed. The suction pipe serves to take up the thread while the twist brake prevents the leading end of the fiber bundle from twisting. In a simple embodiment in accordance with this invention, the twist brake is a mechanical device and is constituted by a surface with a high friction coefficient against which the thread is applied. In addition to or instead of this design of the twist brake as a surface with a high friction coefficient against which the thread is applied, provisions can be made according to invention for the twist brake to be constituted by a sieve subjected to negative air pressure, extending parallel to the conveying direction of the fiber bundle to the suction pipe when the suction pipe is in receiving position.
In order to release the newly formed thread from the twist brake after completed piecing so that it may then be sucked into the suction pipe, said suction pipe is preferably equipped with a switch-over device for the alternate application of negative pressure to the sieve or to the mouth of the suction pipe. In a space-saving embodiment the thread cutting device preferably doubles as the switch-over device.
When the thread forming zone is located in the nip on the other side of the clamping line between the friction spinning elements, opposite to the nip into which the fibers are fed, it is necessary to cover the thread forming zone during piecing and spinning. In this instance the thread forming zone lies open so that the piecing joint does not have to be fed in axial direction of the thread depositing surface. To ensure rather than the thread is rather taken up from the side, a further practical embodiment in accordance with this invention provides for the twist brake to be wedge-shaped in adaptation to the thread forming zone of the friction spinning elements. In this case the twist brake is preferably adjustable with respect to the mouth of the suction pipe as said twist brake is then not limited to the application to only one end of the thread forming zone.
For the piecing joint to be transferred to the mouth of the suction pipe after being taken out of the thread forming zone, provisions are preferably made to prevent such movements in the air stream sucked into the mouth as would be directed counter to the twist brake, so that the piecing joint may be detached easily from the twist brake. For this purpose the mouth of the suction pipe is surrounded by radial clearance. The air fed to the mouth of the suction pipe thus flows axially, and not radially against the twist brake in the latter's vicinity. To ensure this, the axially adjustable twist brake is, in its transferring position, at axial distance from the mouth of the suction pipe.
Instead of a pneumatic grabber, it is also possible to provide a mechanical grabber, consisting preferably of at least two elements which can be moved in relation to each other so as to assume a holding position or a releasing position. For example, one of the elements is constituted by a plurality of garniture needles while the other, movable element is a scraper which moves in the direction of the needle points so as to free the thread previously caught by the garniture needles. The grabber is preferably fashioned as a thread clamp since this is a simple embodiment of the grabber and makes secure release of the thread possible.
As mentioned, it is possible, in accordance with this invention, to produce bobbin beginnings without piecing joints. After beginning of the bobbin however, thread breakgage may occur, and these breaks can then be repaired in the conventional manner without a new bobbin having to be started. For this purpsoe a preferred embodiment in accordance with this invention provides for a thread piecing device, e.g. a knotting or splicing device, to be inserted in the path of the thread between the open-end friction spinning device and the winding device, by means of which the newly pieced thread can be attached to a thread end pulled from the bobbin. However, the device according to this invention is preferably configured so as to make it possible, on the one hand, to piece without piecing thread at the beginning of winding, while not excluding the possibility, on the other hand, of pulling the thread from the bobbin for the purpose of piecing and presentation to the spinning device when thread breakage is to be repaired. In such case it is of advantage if the grabber doubles as a thread feeder, feeding the thread to the open-end friction spinning device.
A variety of designs are possible not only for the grabber, but also for the auxiliary conveying device. If, for example, a suction pipe is used as a grabber, the auxiliary conveying device for the fiber bundle is preferably also constituted by this suction pipe.
Independently of the design of the grabber, the auxiliary conveying device for the fiber bundle, in an alternate embodiment of the object of invention, can consist of a compressed air nozzle directed into the nip and installed on the side of the friction spinning elements which is opposite to the draw-off.
Another embodiment of the auxiliary conveying device is not dependent upon an air stream but is constituted by a thread-like profiling of at least one of the friction elements.
To ensure that the friction spinning elements exert sufficient retention force upon the thread being formed during the spinning process and despite the transporting effect of the friction spinning element's profile, a further embodiment in accordance with this invention provides that the lead of the thread-like profile be coordinated with the thread draw-off speed and with the rotational speed of the friction spinning devices so that the transporting speed achieved by the thread-like profile is lower than the draw-off speed of the thread.
The process as well as the device according to this invention make it possible to piece in a simple manner and without piecing thread. This is especially advantageous for starting the winding of a newly inserted empty tube, as the preparations to ready a piecing thread which are normally required, as well as the mechanical and time expenditures associated therewith, are no longer necessary. Repair of thread breakage is also possible without the normally required piecing thread which is fed back from the bobbin and is introduced into the spinning device, so that it is merely necessary to combine the thread extending toward the bobbin with the newly spun thread in a known manner. On the other hand, further aspects of this invention leave the possibiity open of working without piecing thread when piecing at the start of a bobbin winding and of working with a piecing thread fed back from the bobbin to the spinning aggregate in the conventional manner for the repair of thread breakage. Rational piecing under all operating conditions thus becomes possible.